In areas where the body doesn't resemble what you want or you believe it needs more detail you might need to add new vertices in. There are 3 ways of doing this I will explain below:

Stitching: Though the name is inaccurate to what it actually does. The stitching technique is to delete a vertice and place more vertices in it's place and join them back up again. I usually use this technique if I find a face hungry vertice (a vertice that connects to over six or seven faces) since when it comes to animating, this one vertice will affect a large segment of the mesh.
Usually if I spot one of these vertices I will delete it, create four vertices around where the vertice was and then use 'build face' to stitch up the faces. This technique is also useful for creating vertices where you want but by deleting the verts or edges and placing new vertices where you wanted on your mesh and building the faces again.

Just one thing to remember about creating new vertice's is that when you create them they go back to the default location of where you all the vertices spawn from, so you will have to move the vertices forward or backward so they align with the rest of the body. It is easier to see where they should be by building the faces and then repositioning the vertice's.

Edge Divide: This is the easiest way but can sometimes cause problems. Or position the vertice's where you don't want them. By going to the edge level of edit mesh or editable mesh in the modifier you can click on 'divide' and select an edge. It will then place a vertice in the exact middle of the edge.
The advantage of using this technique is that you will not have to reposition the vertices like with the stitching technique since they are placed where they should but, but they still are in the center of the edge so you do not have as much control as with stitching, but you can always reposition it from there.

Cut: This method can only be used by editable mesh modifier, which requires you to collapse the modifier stack to access it. This technique can be quite helpful at times. Go to the edge level like with edge divide and choose 'cut' and select one edge and then another, it will cut between the two creating another edge, this technique places the vertice exactly where you want it.
Remember not to try to cut at the edge of a face where the vertice is or else it will cut the vertice in two creating two vertice's and you will have to weld those two together again.

Using these three techniques you have major control over your mesh and how to add more detail to it. Below I will mention ways of removing unwanted vertice's instead of creating more:

Target Weld: Target weld is quite effective. To use it from the vertex level select target weld and select and drag (like you would move) a vertice and drag it onto another, it welds the two together. This is good for manually welding vertice's.

Weld Selected: This uses a value in which if you select a bunch of vertice's it will weld all of the vertice's within a certain threshold. This technique is best used for sewing meshes together, such as when you model half of a mesh and then mirror it and sew it together, you can easily select the vertice's in the middle and choose a weld threshold of .5 or 2.0 and weld them together.
It is very effective. The threshold is like a distance radius, if you select it to 2.0 it will weld any selected vertice's within a 2.0 radius. Working out the right radius is up to you, but usually try .5 if it doesn't do it try 2.0 and continue adjusting it to the correct value until you find the most efficient threshold.

Collapse: Collapsing is similar to target weld except that there is no threshold. It will get every vertice you have selected and weld them to the exact center of all of them. This is an effective way of optimizing meshes, selecting a patch of vertice's and collapsing them together.